DESCRIPTION: This proposal aims to elucidate the functioning of neural mechanisms in four domains of complex color and brightness perception. Retinal and early cortical neurons function as efficient encoders and transmitters of stimulus information. This project will study later neural mechanisms that transform this information so that it can be used to determine color appearance, scene segregation, and three-dimensional shape. (1) When a light on a scene changes, objects appear to have systematically different colors, thus potentially providing information about the colors of the objects and the illuminants. The abilities of observers to identity these colors will be measured and related to heuristic based computer algorithms. (2) The spatial configuration of a complex display determines how the color of a region is affected by surrounding regions. Temporal modulation experiments will separate configurational effects on the summation process from gain changes in lateral neural connections. (3) Visual adaptation serves to increase sensitivity to expected changes. For variegated scenes, it is most efficient to adapt the range of sensitivity to the range of stimulation. Experiments will examine the factors that tune this sensitivity and the role of eye movements in the process. (4) Relative velocities help to segregate objects in a scene, and observers can perceive three-dimensional shapes form spatial variations in velocity alone. A set of velocity waves will be used to study the contribution of color and luminance to detecting velocity variations through feature-tracking and motion-energy mechanisms. These experiments will help to identify neural substrates for computational models of scene segmentation and shape inference. The experimental and theoretical results of this project will provide guides for physiological studies of cortical color and luminance mechanisms, and help to understand how problems of visual function are caused by acquired and congenital brain disorders.